1. Field of the Invention
The present invention relates to a direct access storage device (DASD) of the type that includes a spindle motor, and more particularly to improved spindle motor control method and apparatus for a direct access storage device.
2. Description of the Prior Art
Disk drive units incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Typically the disks are mounted in parallel for simultaneous rotation on and by an integrated spindle and motor assembly. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks. Data is recorded in data information tracks arrayed on the surfaces of the disks.
Typically a brushless, direct current (DC), spindle motor is used in disk drives. Two methods for spindle motor control include a linear drive method and a pulse width modulation (PWM) drive method. The PWM drive method has been used to limit the high power dissipation, particularly that occurs at start-up. The linear drive method is the most popular because of its relatively low electrical noise characteristics.
A commercially available driver device part number L6232 manufactured and sold by SGS-Thompson Microelectronics for use in brushless DC motor applications and particularly for use with disk drive applications includes circuitry to perform PWM and linear motor speed control. The spindle driver is described for use to limit the high power dissipation that occurs during spindle start-up through the use of the PWM mode and then to switch to linear motor control during operation at the normal operating spindle speed.
Examples of other known motor control systems are provided by U.S. Pat. Nos. 4,485,337; 4,783,774 and 4,970,610.
U S. Pat. No. 4,485,337 discloses a motor speed control circuit for a disk drive that uses servo data retrieved from a servo disk to regulate the motor speed.
U.S. Pat. No. 4,783,774 discloses a control system for an optical information reproducing apparatus including a circuit for modulating a servo control signal to a pulse width modulation (PWM) signal for driving a disc rotation drive motor or the like with a relatively low power consumption.
U.S. Pat. No. 4,970,610 discloses a spindle motor start routine for a disk drive that supersedes the spindle motor primary control when a stuck condition exists. This control includes a starting reaction torque amplification routine for separating transducer heads that adhere to the disk surface when the disks are not rotated. With the spindle motor starting reaction torque amplification control algorithm, a microprocessor controller attempts to start the spindle motor with a series of increasing duty cycle values of a pulse width modulation signal that is proportional to spindle drive current.
While the prior art motor control systems provide generally effective operation, it is desirable to provide an improved apparatus and method for spindle motor control that reduces the power consumption while providing low electrical noise characteristics.